Asteroid Impact Risk Assessment - NASA

[Pages:28]Asteroid Impact Risk Assessment

Donovan L. Mathias

Asteroid Threat Assessment Project NASA Ames Research Center

USGS Seminar Menlo Park, CA February 27, 2018

ATAP Presentation Contributors

? Michael Aftosmis ? Jessi Dotson ? Marian Nemec ? Darrel Robertson ? Eric Stern ? Lorien Wheeler

February 2018

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Asteroid Threat Assessment

Asteroid Properties

Characterization ? Measurements ? Inference ? Data aggregation ? Property database website

Entry Physics

Entry Simulations & Testing ? Coupled aerothermodynamics ? Ablation & radiation modeling ? Arc jet testing

Surface Hazards

Hazard Simulations ? 3D blast simulations ? Impact crater simulations ? Tsunami simulations ? Thermal radiation models ? Global effects

February 2018

Damage & Risk

Probabilistic Risk Assessment ? Analytic physics-based entry

and damage models ? Probabilistic Monte Carlo

simulation using uncertainty distributions

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Asteroid Characteristics

? Inferring characteristics and

? Meteorites as asteroid samples

distributions

? Bulk density

? Developed distributions of key asteroid characteristics for use in risk models

? Grain density ? Thermal emissivity

? Developing methodology to quantitatively infer characteristics given limited information.

? Acoustic velocity

? Quantifying observed fractures as analog of "aerodynamic strength"

No. of trace lengths cm2 longer than L

Bluff a

102 100 10-2

= 0.186 ?0.013

10-4

10-3

10-2

10-1

100

101

Measured Trace Length (cm)

February 2018

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neoproperties.arc.

? neoproperties website

? Aggregates physical properties of NEOs and meteorites into a searchable database

? Emphasis on properties of interest to the planetary defense community.

? Asteroid contents include:

? Taxonomic class ? Diameters & albedos

? Meteorite contents include:

? Density & porosity ? Compressive & tensile strength ? Elastic & shear moduli ? Heat capacity & thermal conductivity

Feedback? Suggestions? Email jessie.dotson@

February 2018

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Atmospheric Entry

Altitude (km)

February 2018

? ALE3D hydrocode from Lawrence Livermore National Lab. Run in Eulerian mode

? Assumptions: Homogeneous spheres, brittle, no porosity, no ablation

? Provided by Darrel Robertson

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LargeLaMrgeeteMoertoeoidroEidnEtrnytryEEnnvviirronnmmeennt t

Ablation products mix with shock-heated gas in the wake and emit radiation, producing observed light curves and spectra

Flow of melted material

Shock layer radiation out to the surroundings

Strong radiative heat flux to the surface

February 2018

Massive ablation from vaporization produces thick layer of ablation products

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Meteoroid Ablation Experiments

? Asteroid ablation models:

? State of the art asteroid energy deposition code uses single parameter to account for mass loss due to ablation

? Ablation physics for large meteoroids and asteroids is poorly understood

? Development of detailed ablation model:

? Laser scans of pre- and post-test model shapes have provided data for developing and validating melt flow ablation models

? Results indicate much lower melt viscosity than previously assumed

? Widespread melt flow results in significantly lower effective heat of ablation than state of the art

? Looking ahead: luminosity models

? High-resolution spectra of ablation products from arc jet experiment provides unique data for development and valuation of meteoroid luminosity models

February 2018

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